Interval Timer Problem

Hi cris,

I'm using it as a cycle counter.

So I need to change the timeout period to 1sec instead of 1 msec if I want to measure a time round about 0.0008 sec. I also want to measure it exactly as possible.

Thanks is advance for your answer!

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I'm using it as a cycle counter.

So I need to change the timeout period to 1sec instead of 1 msec if I want to measure a time round about 0.0008 sec.

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You definitely need a timeout period larger than the measured time.

As I said above, if your timer is dedicated to the measuring task and doesn't serve other functions or peripherals, you can operate it freely.

So, I suggest this:

- set timeout period larger than the maximum expected interval to be measured

- timer initialized in stopped status

- reset and start the timer when you start your measure,

- stop the timer at the end of measure

- read the duration

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I also want to measure it exactly as possible.

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This greatly depends on your application, namely how you perform the measurement:

- poll a PIO or any other condition and start/stop/read the timer: poor precision, dependent from your polling rate, unless you can afford using the 100% of cpu time for the polling loop and don't execute any other task

- use a irq triggered by start/stop conditions: common solution for greater system effinciency and good precision in the us range

- use a hardware counter solution which automatically identifies start/end conditions and places the measurement in a register which you can read without effort: maximum precision at the expense of a slight increment in hw complexity (fpga resource usage)

Hi cris,

thanks for the help, now it works! I just setup the timeout period to "1sec" and changed a little bit of my code:

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double count_The_Frequency()

{

double total_time_steps=0;

double calculated_time=0;

double calculated_frequency=0;

alt_u32 count_step_1=0x0;

alt_u32 count_step_2=0x0;

int a=0;

//start address of the counter

IOWR_ALTERA_AVALON_TIMER_PERIODH(SYS_CLK_TIMER_BASE,0xFFFF);

IOWR_ALTERA_AVALON_TIMER_PERIODL(SYS_CLK_TIMER_BASE,0xFFFF);

IOWR_ALTERA_AVALON_TIMER_CONTROL(SYS_CLK_TIMER_BASE,ALTERA_AVALON_TIMER_CONTROL_STOP_MSK);

//total_time is in seconds but is measured in ms

//the range depends on the frequency you want to have

//while((total_time<=10) & (total_time>=5)){ //while((total_time<=0.001) & (total_time>=0.00065)){

//by writing to the snapregister you get the data from the counter

IOWR_ALTERA_AVALON_TIMER_SNAPL(SYS_CLK_TIMER_BASE,0x1);

IOWR_ALTERA_AVALON_TIMER_SNAPH(SYS_CLK_TIMER_BASE,0x2);

//start the counter

IOWR_ALTERA_AVALON_TIMER_CONTROL(SYS_CLK_TIMER_BASE,0x06);

//wait till the FAD gives back the right frequency

int j;

for ( j = 0; j < 2; ++j) {

push_The_Button(FAD_CLOCK_BASE);

a=a+1;

IOWR_ALTERA_AVALON_TIMER_SNAPL(SYS_CLK_TIMER_BASE,0x1);

if(a==1){

count_step_1 = IORD_ALTERA_AVALON_TIMER_SNAPH(SYS_CLK_TIMER_BASE)<<16;

count_step_1 =count_step_1|(IORD_ALTERA_AVALON_TIMER_SNAPL(SYS_CLK_TIMER_BASE));

}

if(a==2){

count_step_2 = IORD_ALTERA_AVALON_TIMER_SNAPH(SYS_CLK_TIMER_BASE)<<16;

count_step_2 =count_step_2|(IORD_ALTERA_AVALON_TIMER_SNAPL(SYS_CLK_TIMER_BASE));

}

}

//printf("SnapH : %e\n", (double)IORD_ALTERA_AVALON_TIMER_SNAPH(SYS_CLK_TIMER_BASE));

//stop the counter

IOWR_ALTERA_AVALON_TIMER_CONTROL(SYS_CLK_TIMER_BASE,0x8);

//printf("1; %x\n", count_step_1);

// printf("2: %x \n", count_step_2);

total_time_steps= (count_step_1-count_step_2);

calculated_time= total_time_steps/(50000000);

calculated_frequency=1/calculated_time;

// printf("Frequenz: %e\n", calculated_frequency);

return calculated_frequency;

}

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